crypt: fix crypt writer getting stuck in a loop #902

This happened when the underlying reader returned io.ErrUnexpectedEOF.
The error handling for the call to io.ReadFull failed to take this
into account.

io.ErrUnexpectedEOF is reasonably common when SSL connections go wrong
when communicating with ACD, so it manifested itself as transfers from
non-encrypted ACD to encrypted ACD getting stuck.

crypt/cipher_test.go

@@ -788,6 +788,21 @@ func TestNewEncrypter(t *testing.T) {
 
 }
 
+// Test the stream returning 0, io.ErrUnexpectedEOF - this used to
+// cause a fatal loop
+func TestNewEncrypterErrUnexpectedEOF(t *testing.T) {
+	c, err := newCipher(NameEncryptionStandard, "", "")
+	assert.NoError(t, err)
+
+	in := &errorReader{io.ErrUnexpectedEOF}
+	fh, err := c.newEncrypter(in)
+	assert.NoError(t, err)
+
+	n, err := io.CopyN(ioutil.Discard, fh, 1E6)
+	assert.Equal(t, io.ErrUnexpectedEOF, err)
+	assert.Equal(t, int64(32), n)
+}
+
 type errorReader struct {
 	err error
 }
@@ -854,6 +869,23 @@ func TestNewDecrypter(t *testing.T) {
 	}
 }
 
+// Test the stream returning 0, io.ErrUnexpectedEOF
+func TestNewDecrypterErrUnexpectedEOF(t *testing.T) {
+	c, err := newCipher(NameEncryptionStandard, "", "")
+	assert.NoError(t, err)
+
+	in2 := &errorReader{io.ErrUnexpectedEOF}
+	in1 := bytes.NewBuffer(file16)
+	in := ioutil.NopCloser(io.MultiReader(in1, in2))
+
+	fh, err := c.newDecrypter(in)
+	assert.NoError(t, err)
+
+	n, err := io.CopyN(ioutil.Discard, fh, 1E6)
+	assert.Equal(t, io.ErrUnexpectedEOF, err)
+	assert.Equal(t, int64(16), n)
+}
+
 func TestNewDecrypterSeek(t *testing.T) {
 	c, err := newCipher(NameEncryptionStandard, "", "")
 	assert.NoError(t, err)
@@ -936,8 +968,6 @@ func TestDecrypterRead(t *testing.T) {
 		case i == fileHeaderSize:
 			// This would normally produce an error *except* on the first block
 			expectedErr = nil
-		case i <= fileHeaderSize+blockHeaderSize:
-			expectedErr = ErrorEncryptedFileBadHeader
 		default:
 			expectedErr = io.ErrUnexpectedEOF
 		}